The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally in vehicles, power generated by an engine depends on the amount of air and the amount of fuel introduced into a combustion chamber. In order to increase the power output of the engine, greater amounts of air and fuel can be supplied into the combustion chamber. For this, the size of the combustion chamber may be increased. However, the increased size of the combustion chamber increases the weight and size of the engine.
In the turbocharger, when exhaust gas rotates a turbine wheel of the turbocharger, a wheel of a coaxially-connected air compressor rotates along with the turbine wheel to supply compressed air into the combustion chamber, thereby increasing the power output of the engine. In this manner, the turbocharger can increase the power output of the engine using the exhaust gas that is to be discarded, thereby achieving advantageous effects, such as improved fuel efficiency, the reduced size of the engine, the reduced production of hazardous substances materials, and the increased output power of the engine.
However, the turbocharger has the following problems: when there is only a single passage for exhaust gas, spooling up is delayed at low revolutions per minute (RPMs), and interference occurs between flows of exhaust depending on the sequence of the strokes of the cylinder, thereby lowering efficiency.
In order to overcome this problem, a twin scroll turbocharger is applied, in which an exhaust manifold causing less interference between cylinders is coupled to the turbocharger to form two passages. This configuration removes the interference between flows of exhaust gas, allowing masses of exhaust gas to smoothly flow.
However, in the twin scroll turbocharger, we have discovered that thermal deformation is caused by hot exhaust gas flowing through two passages that diverge from a single passage. That is, when an entrance side of the passage is thermally deformed, a valve intended to close the entrance does not securely contact the entrance, whereby exhaust gas does not properly flow in an intended direction. This consequently decreases the rotation speed of the wheel within the turbocharger, thereby degrading the performance thereof.